Can anyone help please.

I am trying to write a spread sheet to work out overdraft interest charges on every day there is activity on the account. For example over the weekend there are no transactions and the closing balance on Friday will be the same as the opening balance on the following Monday or even Tuesday. Also some days there will be several debit and credit entries in one day. So if I take my bank statement i should be able to compute the overdraft charges as all efforts have failed to match the bank charges so far.

Thanks